Some web processing machines, for example article wrapping machines of the type disclosed in U.S. Pat. Nos. 2,918,769; 3,045,405 and 4,004,400, exert an intermittent pulling force on the web to advance it through the processing machine in step fashion. U.S. Pat. Nos. 2,918,769 and 4,231,560 disclose web unwind stands for feeding webs from a supply roll through a longitudinal web folder to such intermittent advance web processing machines at a rate correlated with the rate of advance of the web by the processing machine. In U.S. Pat. No. 2,918,769, the web supply roll is supported on a pair of drive rollers that are connected through a clutch mechanism to a continuously rotating drive shaft, and the clutch mechanism is operated by a dancer responsive to the tension in the web exiting from the supply roll to start and stop the drive rollers. This supply roll drive is not only relatively complex and expensive to manufacture, but is also subject to wear due to the frequent starting and stopping of the drive rollers. In U.S. Pat. No. 4,231,560 the web is passed from the supply roll over a dancer and part way around an inlet web feed roll before passing to the longitudinal web folders. This apparatus had no provision for controlling unwinding rotation of the web supply roll and, when the web feed was interrupted, the inertia of the web supply roll could cause continued rotation of the supply roll sufficient to allow the web to become slack. It was found that the web in the prior web feed apparatus would sometimes wander or fail to track properly as it passed through the longitudinal folder, and it is believed that the intermittent slackening of the web was a cause of such wandering or improper tracking of the web.
In both U.S. Pat. Nos. 2,918,769 and 4,231,560, feeding of the longitudinally folded web was effected by passing the folded web part way around a feed roller. However, it was found that some wrinkling and creasing occurred when feeding some longitudinally folded webs, particularly relatively heavier weight webs. When a longitudinally folded web is wrapped part way around a roller, the inner layer tends to become slack while the outer layer is tensioned, and it is believed that feeding a folded web by driving the slack inner layer is a cause of such wrinkling and creasing.
Controlling unwinding rotation of a web from a supply roll to an intermittent advance type web processing machine presents special problems. A constant braking action on the web supply rolls is not satisfactory in such applications since constant braking, if adjusted to prevent coasting of the web supply roll when the web feed was interrupted, would correspondingly impede feeding of the web during a feed cycle. Further, the inertia of the web supply rolls varies with the size of the rolls and a constant braking action sufficient to prevent coasting of a full roll would become excessive when the roll size decreased.